Compact high-power ultrashort pulse optical parametric amplification device

Abstract

The invention provides a compact high-power ultrashort pulse optical parametric amplification device. The compact high-power ultrashort pulse optical parametric amplification device is sequentially provided with a slide array, a first blazed grating pair, a slit, a first reflector and a second blazed grating pair in the direction of an optical path, the femtosecond laser is controlled to perform spectrum broadening through the ultrathin slide array, the grating is used for pulse width compression, and the adjustable slit is used for bandwidth selection, so that large-range continuous tuning of optical parameters such as wavelength, pulse width, power and the like of the ultrafast femtosecond laser is realized; the device is especially suitable for high-power hundred-femtosecond and sub-hundred-femtosecond lasers. According to the device, incident femtosecond laser can be efficiently converted, the pulse width and the spectral bandwidth can be greatly and continuously adjusted, and compared with the mode that spectrum broadening is achieved through high-pressure inert gas through femtosecond laser, the laser output stability is remarkably improved; the method is particularly suitable for light source parameter tuning in ultra-high time resolution spectrum testing and ultrafast laser processing systems.

Description

Technical Field

[0001] The invention relates to the field of ultrafast laser technology, and more specifically to a compact high-power ultrashort pulse optical parameter amplifier. Background Art

[0002] Ultrashort pulse laser, also known as ultrafast laser, generally refers to a pulse laser with a pulse width of picoseconds (ps), femtoseconds (fs) or even sub-femtoseconds. The ultra-high instantaneous power and ultra-short pulse width of ultrafast laser make it widely used in micro-nano processing, transient spectroscopy and other fields.

[0003] In the process of laser micro-nano processing, ultrafast lasers act on the surface and interior of different materials to break chemical bonds and achieve "cold processing". However, due to the diversity of materials, different materials have different bond energies and different absorption energy gaps, which inevitably leads to different materials requiring different laser parameter combinations (wavelength, pulse width and power, etc.) to achieve the desired processing effect. This requires the control of the parameters of the laser output laser. Similarly, in the process of transient spectroscopy research, different materials have different band structures, different absorption cross-sections, and different lifetimes of dynamic signals. This also requires the best combination of the wavelength, pulse width and power of the excitation light to achieve the best dynamic signal extraction.

[0004] Among the currently commercialized optical parametric tuning or amplifier products, Lithuanian optical parametric amplifiers (OPA) and nonlinear optical parametric amplifiers (NOPA) are preferred. The two major laser giants in the United States, Coherent and Spectral Physics, have directly purchased these two products from Lithuania for assembly and sale. However, these two products are mainly aimed at the output of titanium sapphire femtosecond lasers. There are few applications in the field of laser processing. In addition, for OPA, it is mainly aimed at wavelength tuning and cannot achieve tuning of pulse width and power. For NOPA, although it can compress the pulse width of the laser, it uses a laser crystal spectrum broadening and compression scheme. The output power is also low while the nonlinear light conversion efficiency is low (usually 10%-30%), and it is generally rarely used in the laser processing process. In particular, these two products are expensive and are usually only equipped in the laboratories of major universities and research institutes. Although the input power of the currently commercially available OPA and NOPA can reach several millijoules, the conversion efficiency of ultra-wideband light through nonlinear effects is low. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a compact high-power ultrashort pulse optical parametric amplifier to overcome the shortcomings of the existing OPA that the pulse width and power cannot be tuned and the existing NOPA that the output power is low under the condition of low nonlinear light conversion efficiency.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions: A compact high-power ultrashort pulse optical parametric amplifier device, which is sequentially arranged along the optical path direction: a glass slide array, a first blazed grating pair, a slit, a first reflector, and a second blazed grating pair; The glass slide array is used to receive incident femtosecond laser light and perform nonlinear spectrum broadening on the incident femtosecond laser light to generate ultra-broadband white light; A first blazed grating pair, used for diffracting the ultra-broadband white light to generate parallel light bands that are continuously distributed in space; A slit, used for selecting a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; a first reflector, used for reflecting the light beam passing through the slit and adjusting the reflection direction of the light beam so as to transmit the light beam to the second blazed grating pair; The second blazed grating pair is used to receive and compress the light beam reflected by the first reflector to generate an output laser. The second blazed grating pair is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

[0007] In one embodiment, the glass slide array includes: at least two groups of glass slides, each glass slide group includes two glass slides, and the glass slides are arranged in sequence along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide in sequence to achieve nonlinear broadening; the angle between the surface of each glass slide and the incident femtosecond laser is at the Brewster angle.

[0008] In one embodiment, the two glass slides in the glass slide set are arranged in a V shape, so that the incident femtosecond laser can propagate along the original optical path after passing through the two glass slides in the glass slide set in sequence.

[0009] In one embodiment, the installation position of the glass slide is constrained by the power of the incident femtosecond laser at the installation position, specifically including:

[0010] in, is the critical power for the glass slide to produce a self-focusing effect; is the power of the incident femtosecond laser at the installation position of the glass slide; the distance between any two adjacent glass slides maintains a minimum distance under the premise of satisfying the incident femtosecond laser power constraint.

[0011] In one embodiment, it further comprises: an inert gas sealed chamber; the inert gas sealed chamber is arranged along the propagation direction of the incident femtosecond laser, and the glass slide array is arranged inside the inert gas sealed chamber along the propagation direction of the incident femtosecond laser; The inert gas sealed chamber is filled with one of helium, neon, argon, krypton or xenon. The gas pressure in the inert gas sealed chamber is .

[0012] In one embodiment, the inert gas sealed cavity is provided with an incident through hole and an exit through hole; The first glass slide in the glass slide array is covered on the incident through hole; The last glass slide in the glass slide array is covered on the exit through hole; The angle between the first glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0013] in, is the Brewster angle of the interface between air and glass slide; is the Brewster angle of the interface between the glass slide and the inert gas; The angle between the last glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0014] in, is the Brewster angle of the interface between the inert gas and the glass slide; is the Brewster angle of the glass slide-air interface.

[0015] In one embodiment, an aperture is further arranged between the glass slide array and the first blazed grating pair to block the halo formed by the diffraction of the incident femtosecond laser, and a through hole is opened at the center of the aperture to allow the ultra-wideband white light located in the central area of ​​the incident femtosecond laser to pass through the through hole and then be emitted into the first blazed grating pair.

[0016] In one embodiment, a concave reflector is further arranged between the aperture and the first blazed grating pair for focusing the divergent ultra-wideband white light passing through the aperture into parallel ultra-wideband white light.

[0017] In one embodiment, the slit includes a first light shielding sheet and a second light shielding sheet; the first light shielding sheet and the second light shielding sheet are both slidably adjustable, and the sliding directions of the first light shielding sheet and the second light shielding sheet are perpendicular to the propagation direction of the parallel light band; The position of the first shading sheet and the position of the second shading sheet are both controlled by motor drive, so that the slit position and the slit width can be continuously adjusted.

[0018] In one embodiment, the first blazed grating pair and the second blazed grating pair are the same blazed grating pair; The first blazed grating pair comprises: A first blazed grating, used for diffracting the ultra-broadband white light into a light band continuously distributed in space; A second blazed grating, used to adjust the propagation angle of the light band to generate parallel light bands that are continuously distributed in space; The angle between the first blazed grating and the ultra-wideband white light is the Littrow angle; the second blazed grating is in a sliding arrangement, and the sliding distance of the second blazed grating is controlled by a motor drive to adjust the optical path length of each wavelength of light in the light band; The second blazed grating is further used to receive the light beam reflected by the first reflector and transmit the light beam back to the first blazed grating. The first blazed grating is further used to compress the light beam to generate an outgoing femtosecond laser.

[0019] In summary, the present invention has the following beneficial effects: a compact high-power ultrashort pulse optical parametric amplifier, which is provided with: a glass slide array, a first blazed grating pair, a slit, a first reflector, and a second blazed grating pair in sequence along the optical path direction; the glass slide array is used to receive incident femtosecond laser light and perform nonlinear spectrum broadening on the incident femtosecond laser light to generate ultra-wideband white light; the first blazed grating pair is used to diffract the ultra-wideband white light to generate parallel light bands distributed continuously in space; the slit is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; the first reflector is used to reflect the light beam passing through the slit. The invention relates to a method for controlling a femtosecond laser to transmit a light beam reflected by a slit, and adjusting the reflection direction of the light beam to transmit the light beam to a second blazed grating pair; the second blazed grating pair is used to receive and compress the light beam reflected by the first reflector to generate an outgoing laser, and the second blazed grating pair is also used to perform dispersion compensation on the received light beam to achieve pulse width compression; the present application controls the femtosecond laser to perform spectrum broadening through an ultra-thin glass array, uses a grating pair to perform pulse width compression, and uses an adjustable slit to perform bandwidth selection, thereby achieving a wide range of continuous tuning of optical parameters such as wavelength, pulse width, and power of the ultrafast femtosecond laser, and is particularly suitable for high-power hundred-femtosecond and sub-hundred-femtosecond lasers. The present device can efficiently convert incident femtosecond lasers, and the pulse width and spectral bandwidth can be greatly and continuously adjusted. Compared with the method of using a femtosecond laser to achieve spectrum broadening through a high-pressure inert gas, the stability of the laser output is significantly improved; it is particularly suitable for tuning light source parameters in ultra-high time-resolution spectrum testing and ultrafast laser processing systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of a compact high-power ultrashort pulse optical parametric amplifier device of the present invention; Figure 2 Schematic diagram of light propagation when four slides are arranged in parallel; Figure 3 A schematic diagram of light propagation when four glass slides are arranged in a V shape in the present invention; Figure 4 It is a schematic diagram of the structure in which four glass slides are installed in an inert gas sealed chamber in the present invention; Figure 5 A schematic diagram of calculating the rotation angle of the first reflector in the present invention; In the figure: 11, first glass slide; 12, second glass slide; 21, first blazed grating; 22, second blazed grating; 3, slit; 4, first reflector; 5, exit mirror; 6, concave reflector; 7, second reflector; 8, inert gas sealed chamber. DETAILED DESCRIPTION

[0021] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. Several embodiments of the present invention are shown in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0022] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0023] In order to facilitate the understanding of the technical solution of this patent by those skilled in the art, the prior art in this field is first described: Ultrashort pulse laser, also known as ultrafast laser, generally refers to a pulse laser with a pulse width of picoseconds (ps), femtoseconds (fs) or even sub-femtoseconds. The ultra-high instantaneous power and ultra-short pulse width of ultrafast laser make it widely used in micro-nano processing, transient spectroscopy and other fields.

[0024] OPA (Optical Parametric Amplifier) ​​is a device based on nonlinear optical effects, mainly used to amplify and tune the wavelength of laser signals within a specific wavelength range. The main working principle of OPA relies on the optical parametric amplification effect of nonlinear crystals. OPA generates different frequency components in the output light through interaction with pump light. The working principle of OPA mainly includes: the input signal interacts with the pump light through a nonlinear process to generate a new signal light (output light). This process usually occurs in a nonlinear crystal, and its nonlinear properties are used to amplify the signal light (or enhance weak light signals). The gain process of OPA mainly affects the intensity of the signal light, but does not directly change the temporal characteristics (pulse width) of the light. Although in some cases, OPA will produce some dispersion effects through interaction with pump light, this usually does not significantly change the pulse width. The gain efficiency of OPA is related to the power of the pump light and the initial intensity of the signal light. By increasing the power of the pump light, the power of the signal light can be increased, but the gain amplitude of OPA does not precisely control the power. The output power of the OPA is related to the power of the pump light and the efficiency of the nonlinear crystal, so its output power is determined by the characteristics of the pump and the crystal.

[0025] The gain process of the NOPA (Non-Linear Optical Parametric Amplifier) ​​system involves converting the pump light energy into signal light and idler light. The phase matching condition in the nonlinear optical process determines the energy exchange efficiency between the pump light and the signal light. Due to the strict requirements of the phase matching condition on the wavelength and beam shape, a perfect match cannot be achieved, which limits the effective conversion of energy. Different nonlinear crystal materials have different nonlinear coefficients, losses, and bandwidth characteristics. For efficient spectral broadening and compression, it is very important to choose the right crystal material, but these materials usually need to work at lower conversion efficiency. Due to the low nonlinear light conversion efficiency of NOPA, usually only , resulting in a relatively low power output signal, usually only a few millijoules.

[0026] Embodiment 1 In order to solve the above problems, the present invention provides a compact high-power ultrashort pulse optical parametric amplifier, such as Figure 1-3 As shown, arranged in sequence along the optical path direction are: a glass slide array, a first blazed grating pair, a slit 3, a first reflector 4, and a second blazed grating pair; The glass slide array is used to receive incident femtosecond laser light and perform nonlinear spectrum broadening on the incident femtosecond laser light to generate ultra-broadband white light; A first blazed grating pair, used for diffracting the ultra-broadband white light to generate parallel light bands that are continuously distributed in space; Slit 3, used for selecting a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; a first reflector 4, used for reflecting the light beam passing through the slit 3 and adjusting the reflection direction of the light beam so as to transmit the light beam to the second blazed grating pair; The second blazed grating pair is used to receive and compress the light beam reflected by the first reflector 4 to generate an outgoing laser. The second blazed grating pair is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

[0027] In practical applications, multiple glass slides are arranged in the glass slide array, which can perform nonlinear broadening of the incident laser when receiving the incident laser. When the incident laser passes through the glass slide, the instantaneous phase of the pulse will change, causing the spectrum to expand to the low-frequency and high-frequency sides respectively, thereby broadening the pulse of the incident laser and generating ultra-wideband white light. Under the condition of fixed incident laser parameters, the broadening amplitude of ultra-wideband white light is related to the glass slide material, glass slide thickness, gas pressure in the environment where the glass slide is located, and gas type.

[0028] The first blazed grating pair is used to diffract the ultra-broadband white light to generate a light band that is continuously distributed in space. In order to select a preset central wavelength and a light beam with a preset bandwidth range from the light band, the first blazed grating pair is also needed to adjust the light band that is continuously distributed in space into a parallel light band. By adjusting the distance within the first blazed grating pair, the optical path can also be compensated, so that the optical path of the light with a longer wavelength becomes longer and the optical path of the light with a shorter wavelength becomes shorter, so that the light of each wavelength can be kept in a closer position to compress the pulse width of the incident laser.

[0029] The slit 3 is used to select a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band. Since the parallel light band is continuously distributed in space, adjusting the position of the slit 3 can correspond to selecting the light band with a preset central wavelength. According to the Fourier transform limit formula, and By adjusting the bandwidth and wavelength position, the pulse width can be adjusted. The center position of slit 3 corresponds to the center wavelength, and the width of slit 3 is proportional to the wavelength bandwidth of the reflected light band. At the same time, the change of wavelength bandwidth will also cause the change of output laser power. Therefore, the optical parameters such as the center wavelength, bandwidth, pulse width, power, etc. of the laser can be continuously tuned.

[0030] The first reflector 4 is used to adjust the angle of the wide band of light passing through the slit 3 so that the propagation direction of the wide band of light is separated from the direction of the incident light.

[0031] The second blazed grating pair is used to receive and compress the light beam reflected by the first reflector 4 to generate an outgoing laser. The second blazed grating pair is also used to perform dispersion compensation on the received light beam to achieve a pulse width compressed light beam.

[0032] In summary, the present application provides a compact high-power ultrashort pulse optical parametric amplifier, which uses a femtosecond laser to perform spectrum broadening through an ultra-thin glass slide and a grating pair to perform pulse width compression and bandwidth selection, and is particularly suitable for high-power hundred-femtosecond and sub-hundred-femtosecond lasers. The input light conversion efficiency of the device is high, and the pulse width and spectral bandwidth can be greatly continuously adjustable. After the spectrum is doubled and the difference frequency is performed, the wavelength adjustable range can be wider. Compared with the method of using a femtosecond laser to achieve spectrum broadening only through high-pressure inert gas, the stability of the laser output is greatly improved. At the same time, compared with the solution of using expensive ultra-wideband chirped mirrors for compression, the product price is greatly reduced. It is particularly suitable for light source parameter tuning in ultra-high time-resolution spectral testing and ultrafast laser processing systems.

[0033] In one embodiment, the glass slide array includes: at least two groups of glass slides, each glass slide group includes two glass slides, and the glass slides are arranged in sequence along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide in sequence to achieve nonlinear broadening; the angle between the surface of each glass slide and the incident femtosecond laser is at the Brewster angle.

[0034] In practical applications, Brewster's Angle refers to the angle at which the reflected light is completely polarized and the power of the transmitted light is maximized when the incident angle meets certain conditions when light is incident from one medium to another. The specific angle of Brewster's Angle is related to the refractive index of the two media, specifically satisfying:

[0035] in, represents the Brewster angle, which is the angle between the incident light and the interface; is the refractive index of the incident medium; is the refractive index of the transmission medium. When light is incident from air to the glass slide, part of the light will be reflected and part of the light will be transmitted. The intensity of the reflected light and the transmitted light depends on the incident angle. At the Brewster angle, the intensity of the reflected light is minimized and the intensity of the transmitted light is maximized. Therefore, controlling the angle between the glass slide and the incident femtosecond laser can effectively improve the transmission efficiency of the incident femtosecond laser.

[0036] In one embodiment, the first glass slide 11 and the second glass slide 12 in the glass slide set are arranged in a V shape, so that the incident femtosecond laser can propagate along the original optical path after passing through the two glass slides in the glass slide set in sequence.

[0037] In practical applications, such as Figure 2 , Figure 3 As shown, the two glass slides in each glass slide group are arranged in a V shape, so that the laser can be deflected in the thick glass slide and then undergo a slight optical path correction, thereby avoiding a large position offset between the optical path and the original incident femtosecond laser, which would affect the integration of the device.

[0038] In one embodiment, the installation position of the glass slide is constrained by the power of the incident femtosecond laser at the installation position, specifically including:

[0039] in, is the critical power for the glass slide to produce a self-focusing effect; is the power of the incident femtosecond laser at the installation position of the glass slide; the distance between any two adjacent glass slides maintains a minimum distance under the premise of satisfying the incident femtosecond laser power constraint.

[0040] In practical applications, when ultrashort lasers propagate in the air, due to the high intensity of the laser, the refractive index of the air will change, usually increasing. This change will cause the laser beam to focus, further increasing its intensity and forming a self-focusing effect. After focusing, ultrashort laser pulses usually form a high-intensity concentrated light spot in the near-focus area. As the laser propagates, the focus will expand. However, the high intensity and nonlinear effects of the laser pulse may cause the laser to refocus or deform in the area away from the focus, forming a layered propagation effect, that is, the layered effect of laser propagation in the air. Therefore, during the propagation process, the laser usually focuses-diverges-focuses alternately, and the laser will form numerous focal spots on the propagation optical path. Because the thinner the laser beam, the higher the peak power of the laser, the more obvious the nonlinear effect of the interaction between the laser and the glass slide. The peak power cannot be too high, as too high peak power will damage the glass slide. When setting the position of the glass slide, it is usually necessary to set the glass slide near the focal spot position to balance the relationship between the nonlinear effect and the peak power. Specifically, the position of the glass slide can be adjusted to achieve the maximum value of the spectrum broadening at the position of the glass slide.

[0041] Based on the hierarchical effect of the nonlinear laser, it is necessary to determine the power of the incident femtosecond laser at each position. , and the critical power of the self-focusing effect of the glass slide , to determine the placement of the slide, that is, it is necessary to meet the requirements at the placement position. In order to improve the integration of the device and reduce the size of the device, it is necessary to control the distance between the two glass slides to be kept at a minimum value when the glass slides are placed while satisfying the incident power. The position of the glass slide can also be adjusted to achieve the maximum value of the spectrum broadening at the position of the glass slide.

[0042] In one embodiment, the glass slide is made of one or more of BBO crystal, sapphire crystal, and quartz glass.

[0043] In practical applications, the power of the input ultrashort laser is controlled so that the peak power threshold of the input ultrashort laser pulse is Greater than the power threshold for glass slides to achieve self-phase modulation (SPM) The refractive index of the material that the glass slide or laser passes through has nonlinear characteristics. The refractive index n of the optical material is related to the light intensity I. When the electric field intensity changes, the refractive index of the material also changes, and the phase of the light wave passing through the medium also changes. This is SPM. The frequency adjustment caused by SPM broadens the spectrum. Its frequency shift It can be expressed as follows:

[0044]

[0045] in, is the average laser power, is the laser repetition frequency, is the focal spot area, is the single pulse duration, is the laser wavelength, is the effective area, is the effective length, is the nonlinear refractive index of the medium. At the same time, the power threshold of the input laser It must be greater than the critical power for the glass slide to produce self-focusing effect , but less than twice the latter, specifically satisfying:

[0046]

[0047] Where λ is the laser wavelength, is the linear refractive index, is the nonlinear refractive index of the medium. By changing the glass slides of different materials and thicknesses, the spectrum can achieve a bandwidth broadening of 10 times or more. In particular, the ultra-thin micron-level glass slide design is more suitable for high-peak power femtosecond laser spectrum broadening than the currently commonly used spectrum broadening designs, such as sapphire, CaF2, water film, etc.

[0048] In one embodiment, the thickness of the glass slides of the glass slide array can be adjusted according to the pulse energy of the incident femtosecond laser. From the perspective of bandwidth broadening and the quality of supercontinuum light generated, the higher the power, the thinner the glass slide, so that the thickness of the medium through which the laser passes is small, which is conducive to reducing the divergence of the laser and improving the beam quality. In this embodiment, the thickness of the glass slide is between . Angle of incidence The Brewster angle is satisfied. Using the currently commercial titanium sapphire laser as the light source, the output laser pulse width is , the output power is , the repetition frequency is The device can achieve an input power of By adjusting the focal length of the laser passing through the concave mirror, the highest peak power at the shorter point can be achieved. By adjusting the position of the glass slide at the focus, the glass slide can be placed at the best peak power position to obtain the best widening effect and conversion efficiency without damaging the glass slide. After the slides are assembled, The conversion efficiency of ultra-broadband white light generated by the input laser can reach When injected into the slide cavity Atmosphere pressure of inert gas He, the spectrum width can reach In this application, the optical signal passes through the slit 3 and is reflected by the first reflector 4, and then is compressed by the blazed grating. The pulse width can be continuously tuned from sub-5 femtoseconds to picoseconds, and the central wavelength and bandwidth can be adjusted in the range of 1.5 Å. By combining the doubled and difference frequency lasers, and selecting the frequency through the slit 3 and the first reflector 4, a large continuous adjustment can be achieved in the wavelength band from ultraviolet 250nm to infrared 1700nm.

[0049] In one embodiment, Figure 4 As shown, it also includes: an inert gas sealed chamber 8; the inert gas sealed chamber 8 is arranged along the propagation direction of the incident femtosecond laser, and the glass slide array is arranged inside the inert gas sealed chamber 8 along the propagation direction of the incident femtosecond laser; The inert gas sealed chamber 8 is filled with one of helium, neon, argon, krypton or xenon. The gas pressure in the inert gas sealed chamber 8 is .

[0050] Specifically, in practical applications, the spectrum broadening effect is related to the medium through which the ultrafast laser passes. In an inert gas, the broadening effect of the ultrafast laser is more obvious than in an air medium, and in a gas medium, the greater the pressure of the gas medium, the greater the effect on the spectrum broadening. Therefore, by filling the inert gas sealed cavity 8 with an inert gas and controlling the pressure of the inert gas in the sealed cavity, the broadening effect of the ultrafast laser can be further improved. In the process of the laser passing through the glass slide group, the glass slide and the inert gas can both serve as nonlinear media and have a broadening effect on the laser. In particular, the nonlinear refractive index of the inert gas increases with the increase of the gas pressure, thereby having a positive gain effect on the broadening of the spectrum.

[0051] In one embodiment, Figure 4 As shown, the inert gas sealed chamber 8 is provided with an incident through hole and an exit through hole; The first glass slide in the glass slide array is covered on the incident through hole; The last glass slide in the glass slide array is covered on the exit through hole; The angle between the first glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0052] in, is the Brewster angle of the interface between air and glass slide; is the Brewster angle of the interface between the glass slide and the inert gas; The angle between the last glass slide in the glass slide array and the incident femtosecond laser satisfy:

[0053] in, is the Brewster angle of the interface between the inert gas and the glass slide; is the Brewster angle of the glass slide-air interface.

[0054] Specifically, when high-pressure inert gas is filled into the inert gas sealed chamber 8, the effect of ultrafast laser spectrum broadening is improved, and the Brewster angle of the ultrafast femtosecond laser incident from the glass slide to the high-pressure inert gas is changed. That is, on the first glass slide, the first Brewster angle of the ultrafast femtosecond laser incident from the air to the glass slide is , and the second Brewster angle of ultrafast femtosecond laser emitted from the glass slide into the inert gas In order to maximize the transmittance of the femtosecond laser, the average of the two Brewster angles can be taken. Similarly, the angle of the last slide also needs to be determined based on the average of the two Brewster angles.

[0055] In the inert gas sealed chamber 8, in order to prevent the high-pressure gas from crushing the glass slide on the incident through hole, the sizes of the incident through hole and the exit through hole need to be controlled within a predetermined size range, usually 1 mm to 3 mm.

[0056] Under one atmosphere of pressure, when the laser is refracted on the surface and inside of the glass slide through the inert gas medium, the refractive index of the inert gas is similar to that of air. However, the refractive index of the inert gas increases with the increase of gas pressure, thereby fine-tuning the direction of the laser emitted through the glass slide group.

[0057] Changes in the refractive index of noble gases ,satisfy:

[0058] in , and Refractive index, gas pressure and temperature under standard conditions. and are the expansion coefficient and temperature in Celsius of the gas respectively. It is the increase or change of gas pressure. By changing the gas pressure, the refractive index also changes proportionally, thereby modulating the Brewster angle. Under the same laser input parameters, if the inert gas He is replaced by Ne gas with a larger nonlinear refractive index, or even Xe gas, the spectrum broadening will be further increased to reach .

[0059] In one embodiment, the glass slide is detachable so that the material and thickness of the glass slide can be adjusted according to the pulse energy of the incident laser. From the perspective of bandwidth broadening and the quality of supercontinuum light generated, the higher the power, the thinner the glass slide, so that the thickness of the medium through which the laser passes is small, which is conducive to reducing the divergence of the laser and improving the beam quality.

[0060] In one embodiment, an aperture is further arranged between the glass slide array and the first blazed grating pair to block the halo formed by the diffraction of the incident femtosecond laser, and a through hole is opened at the center of the aperture to allow the ultra-wideband white light located in the central area of ​​the incident femtosecond laser to pass through the through hole and then be emitted into the first blazed grating pair.

[0061] After passing through the glass slide, the ultrafast femtosecond laser will have its spectrum broadened and a colored halo will be generated around the laser. These colored halos may interfere with subsequent light after entering the grating. To solve this problem, an aperture with a through hole is needed to shield the colored halo around the laser and only allow the white light in the middle of the ultrafast femtosecond laser to pass through, while also being able to adjust the laser power.

[0062] In one embodiment, a concave reflector 6 is further provided between the aperture and the first blazed grating pair for focusing the divergent ultra-wideband white light passing through the aperture into parallel ultra-wideband white light.

[0063] Since the ultrafast laser will produce a layering effect when propagating in the medium, it will diverge after passing through the last glass slide. Therefore, the ultrafast laser will still diverge after passing through the aperture. In order to allow the ultrafast laser to propagate smoothly backward, a concave reflector 6 is required to be set on the propagation light path of the ultrafast laser to focus the divergent ultra-broadband white light into parallel ultra-broadband white light. The spot diameter on the concave reflector 6 is The following constraints need to be met:

[0064] in is the maximum diameter of the light spot on the concave reflector 6; is the focal length of the concave reflector 6; is the central wavelength of the incident light beam; is the focal spot radius where the last slide is located.

[0065] In one embodiment, in order to adjust the angle of the light beam reflected by the concave reflecting mirror 6 , a second reflecting mirror 7 for adjusting the propagation direction of the parallel ultra-wideband white light is further arranged behind the concave reflecting mirror 6 .

[0066] In one embodiment, the slit 3 includes a first shading sheet and a second shading sheet; the first shading sheet and the second shading sheet can both be slidably adjusted, and the sliding directions of the first shading sheet and the second shading sheet are perpendicular to the propagation direction of the parallel light band; the position of the first shading sheet and the position of the second shading sheet are both controlled by a motor drive to achieve continuous adjustment of the position and width of the slit 3.

[0067] The sliding position of the first shading sheet and the second shading sheet is controlled by a motor drive to achieve continuous adjustment of the position and width of slit 3, which is highly flexible and adaptable. The sliding direction of the shading sheet is perpendicular to the propagation direction of the parallel light band, which can efficiently cut the target spectral area, avoid lateral interference, and improve the adjustment efficiency. Using a servo motor or stepper motor drive, the motor rotation angle is accurately controlled based on the number of pulses, thereby achieving high-precision adjustment of the position and width of slit 3 to meet different experimental needs. The motor drive supports automated adjustment, simplifies the operating process, and reduces manual intervention. It is particularly suitable for application scenarios that require frequent switching of spectral settings, significantly improving the convenience and efficiency of the system.

[0068] In practical applications, the slit 3 can be adjusted manually or electrically, and the slit 3 can be adjusted by changing the position of the center point of the slit 3 to select the position of the central wavelength, or by adjusting the width of the slit 3 to select the bandwidth of the optical signal passing through the slit 3. Among them, the selection of the position of the central wavelength requires the overall adjustment of the upper and lower shading plates of the slit 3. While keeping the phase position unchanged, the two shading plates are moved simultaneously to achieve the selection of the central wavelength of the slit 3. The selection of the bandwidth is to control the relative position of the upper and lower shading plates of the slit 3 to adjust the width of the slit 3. According to the time-frequency uncertainty principle, the bandwidth of an ultrafast laser is inversely proportional to the pulse width. Therefore, by selecting the bandwidth of the light band formed by the broadening of the ultrafast laser, the pulse width of the ultrafast laser can be indirectly controlled. In the present application, the optical signal passing through the slit 3 and reflected by the first reflector 4, after the pulse width compression by the blazed grating, the pulse width can be continuously tuned between sub-5 femtoseconds and picoseconds, and the central wavelength and bandwidth can be adjusted within a certain range. Combined with the frequency-doubled and frequency-differenced lasers, the integrated frequency selection through the slit 3-first reflector 4 can achieve the goal of switching from ultraviolet to arrive Largely continuously adjustable within the infrared band.

[0069] In one embodiment, the first blazed grating pair and the second blazed grating pair are the same blazed grating pair; The first blazed grating pair comprises: A first blazed grating 21, used for diffracting the ultra-broadband white light into a light band continuously distributed in space; A second blazed grating 22, used to adjust the propagation angle of the light band to generate parallel light bands that are continuously distributed in space; The angle between the first blazed grating 21 and the ultra-wideband white light is the Littrow angle; the second blazed grating 22 is a sliding arrangement, and the sliding distance of the second blazed grating 22 is controlled by a motor drive to adjust the optical path length of each wavelength of light in the light band; The second blazed grating 22 is further used to receive the light beam reflected by the first reflector 4 and transmit the light beam back to the first blazed grating 21. The first blazed grating 21 is further used to compress the light beam to generate an outgoing femtosecond laser.

[0070] In practical applications, the first blazed grating is used to diffract the ultra-broadband white light into a light band that is continuously distributed in space, and the second blazed grating is used to parallelize the light band to generate parallel light bands that are continuously distributed in space, such as Figure 1As shown, although there is a certain angle between the multiple light beams emitted by the first blazed grating, the second blazed grating can adjust the angular relationship between the light beams so that the light beams with angles are converted into mutually parallel light beams. In applications requiring high-precision focusing, interference, laser beam transmission, etc., parallel light beams can improve the efficiency and controllability of the system. By converting the light beams that originally have a certain angle relationship into parallel light beams, the propagation direction and coherence of the light can be optimized. Through two-stage grating processing, the first grating realizes the decomposition of the spectrum, and the second grating completes the task of parallelizing the light beam, so that the configuration of the light source can adapt to different optical system design requirements. Parallelizing the light beam can also make it easier to calculate the corresponding position and size to control the slit 3 when controlling the movement of the slit 3 to select part of the light signal for pulse width compression. In addition, parallelizing the light beam can also facilitate the calculation of the optical path to adjust the angle of the first reflector 4 to achieve pulse width compression of the ultrafast laser. In addition, the second blazed grating can also slide, and the distance between the second blazed grating and the first grating can be adjusted to adjust the optical path of light bands of different wavelengths to compress the pulse width of the ultrafast laser.

[0071] In one embodiment, the angle between the first blazed grating 21 and the ultra-wideband white light complies with the Littrow angle.

[0072] In practical applications, the grating constant is usually tens to thousands of grids / mm. By adjusting the grating spacing, the pulse width of the broadened spectrum can be compressed. The incident blazed grating angle satisfies the Littrow angle. ,in is the diffraction order, is the wavelength, is the grating constant, which is the number of grating lines per millimeter. is the incident angle. When the incident angle is equal to the Littrow angle, the diffraction efficiency of the grating is the highest.

[0073] In one embodiment, the first reflector 4 is rotatably arranged to adjust the position misalignment of the light spot of the light beam after passing through the slit 3 and reaching the laser incident first grating, thereby ensuring the output of the laser and preventing it from returning to the original path.

[0074] Specifically, if Figure 5 The rotation angle of the first reflector 4 needs to be determined according to the offset of the light spot, such as Figure 5 As shown, ultra-broadband white light irradiates the first grating to form a light spot A. When the first reflector 4 reflects the light beam, a light spot B is formed on the second grating, and then a light spot C is formed after being reflected by the second grating to the first grating. Therefore, the rotation angle of the first reflector 4 is satisfy:

[0075]

[0076]

[0077] in, represents the distance between the light spot A and the light spot C, is the vertical distance between the two gratings; It represents the distance from the center point of the light spot B to the foot of the perpendicular D formed by the second grating and the light spot A. In summary, according to the distance between the two gratings , and the distance that the spot formed by the outgoing laser on the first grating needs to move , the angle that the first reflector 4 needs to rotate can be calculated .

[0078] In one embodiment, an output mirror 5 is further included. The output mirror 5 is arranged behind the first blazed grating 21 and is used to receive the output femtosecond laser and adjust the direction and angle of the output femtosecond laser.

[0079] In summary, the present application proposes a high-power ultrashort pulse optical parametric amplifier. The present application controls the femtosecond laser to perform spectrum broadening through an ultra-thin glass slide, pulse width compression through a grating pair, and frequency bandwidth selection to perform optical parameter tuning, which is particularly suitable for high-power hundred-femtosecond and sub-hundred-femtosecond lasers. The device of the present application can efficiently convert the incident femtosecond laser, and the pulse width and spectral bandwidth can be greatly continuously adjustable. Compared with the method of using a femtosecond laser to achieve spectrum broadening through a high-pressure inert gas, the stability of the laser output is greatly improved, and compared with the scheme of using an expensive ultra-wideband chirped mirror for compression, the product price is greatly reduced; it is particularly suitable for tuning the light source parameters in ultra-high time-resolution spectral testing and ultrafast laser processing systems.

[0080] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A compact high-power ultrashort pulse optical parametric amplifier, characterized in that: Arranged in sequence along the optical path direction are: a glass slide array, a first blazed grating pair, a slit, a first reflector, and a second blazed grating pair; The glass slide array is used to receive incident femtosecond laser light and perform nonlinear spectrum broadening on the incident femtosecond laser light to generate ultra-broadband white light; A first blazed grating pair, used for diffracting the ultra-broadband white light to generate parallel light bands that are continuously distributed in space; A slit, used for selecting a light beam with a preset central wavelength and a preset bandwidth range from the parallel light band; a first reflector, used for reflecting the light beam passing through the slit and adjusting the reflection direction of the light beam so as to transmit the light beam to the second blazed grating pair; The second blazed grating pair is used to receive and compress the light beam reflected by the first reflector to generate an output laser. The second blazed grating pair is also used to perform dispersion compensation on the received light beam to achieve pulse width compression.

2. A compact high-power ultrashort pulse optical parametric amplifier according to claim 1, characterized in that: The glass slide array includes: at least two groups of glass slides, each glass slide group includes two glass slides, and the glass slides are arranged in sequence along the propagation direction of the incident femtosecond laser, so that the incident femtosecond laser passes through each glass slide in sequence to achieve nonlinear broadening; the angle between the surface of each glass slide and the incident femtosecond laser is at the Brewster angle.

3. A compact high-power ultrashort pulse optical parametric amplifier according to claim 2, characterized in that: The two glass slides in the glass slide group are arranged in a V shape, so that the incident femtosecond laser can propagate along the original light path after passing through the two glass slides in the glass slide group in sequence.

4. A compact high-power ultrashort pulse optical parametric amplifier according to claim 3, characterized in that: The installation position of the glass slide is constrained by the power of the incident femtosecond laser at the installation position, specifically including: in, is the critical power for the glass slide to produce a self-focusing effect; is the power of the incident femtosecond laser at the installation position of the glass slide; the distance between any two adjacent glass slides maintains a minimum distance under the premise of satisfying the incident femtosecond laser power constraint.

5. The compact high-power ultrashort pulse optical parametric amplifier according to claim 1, characterized in that: Also includes: An inert gas sealed chamber; the inert gas sealed chamber is arranged along the propagation direction of the incident femtosecond laser, and the glass slide array is arranged inside the inert gas sealed chamber along the propagation direction of the incident femtosecond laser; The inert gas sealed chamber is filled with one of helium, neon, argon, krypton or xenon. The gas pressure in the inert gas sealed chamber is .

6. A compact high-power ultrashort pulse optical parametric amplifier according to claim 5, characterized in that: The inert gas sealed cavity is provided with an incident through hole and an exit through hole; The first glass slide in the glass slide array is covered on the incident through hole; The last glass slide in the glass slide array is covered on the exit through hole; The angle between the first glass slide in the glass slide array and the incident femtosecond laser satisfy: in, is the Brewster angle of the interface between air and glass slide; is the Brewster angle of the interface between the glass slide and the inert gas; The angle between the last glass slide in the glass slide array and the incident femtosecond laser satisfy: in, is the Brewster angle of the interface between the inert gas and the glass slide; is the Brewster angle of the glass slide-air interface.

7. The compact high-power ultrashort pulse optical parametric amplifier according to claim 1, characterized in that: An aperture is also arranged between the glass slide array and the first blazed grating pair to block the halo formed by the diffraction of the incident femtosecond laser. A through hole is opened at the center of the aperture to allow the ultra-wideband white light located in the central area of ​​the incident femtosecond laser to pass through the through hole and then enter the first blazed grating pair.

8. The compact high-power ultrashort pulse optical parametric amplifier according to claim 7, characterized in that: A concave reflector is also arranged between the aperture and the first blazed grating pair, for focusing the divergent ultra-wideband white light passing through the aperture into parallel ultra-wideband white light.

9. The compact high-power ultrashort pulse optical parametric amplifier according to claim 1, characterized in that: The slit includes a first light shielding sheet and a second light shielding sheet; the first light shielding sheet and the second light shielding sheet are both capable of sliding and adjusting, and the sliding directions of the first light shielding sheet and the second light shielding sheet are perpendicular to the propagation direction of the parallel light band; The position of the first shading sheet and the position of the second shading sheet are both controlled by motor drive, so that the slit position and the slit width can be continuously adjusted.

10. The compact high-power ultrashort pulse optical parametric amplifier according to claim 1, characterized in that: The first blazed grating pair and the second blazed grating pair are the same blazed grating pair; The first blazed grating pair comprises: A first blazed grating, used for diffracting the ultra-broadband white light into a light band continuously distributed in space; A second blazed grating, used to adjust the propagation angle of the light band to generate parallel light bands that are continuously distributed in space; The angle between the first blazed grating and the ultra-wideband white light is the Littrow angle; the second blazed grating is in a sliding arrangement, and the sliding distance of the second blazed grating is controlled by a motor drive to adjust the optical path length of each wavelength of light in the light band; The second blazed grating is further used to receive the light beam reflected by the first reflector and transmit the light beam back to the first blazed grating. The first blazed grating is further used to compress the light beam to generate an outgoing femtosecond laser.

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